This invention relates generally to cathode ray tube (CRT) display systems and specifically to CRT display systems that are operated in a standby mode for substantial periods of time.
The use of CRT terminals has grown dramatically with increased acceptance of computers, word processors, automatic banking systems and a myriad of other consumer applications involving video displays. In a large number of applications, the actual utilization time of the CRT terminal, that is the time when a viewer is present and either observing or using the terminal, is relatively small in comparison with the time in which the terminal is on, but not in use or being viewed.
The CRTs and the light-emitting phosphors comprising their viewing screens have finite service lives which are related to the degree of their usage. CRTs that are subject to high brightness use generally experience correspondingly shorter useful phosphor life than those subject to low brightness operation. It is also well known that the bright stationary display patterns may permanently damage the phosphor viewing screen. Another factor worthy of note is that the power consumed by the CRT display system is the major component of the total power consumption of the terminal.
A co-pending application of the inventor, (D4924) Ser. No. 559,166, filed Dec. 7, 1983, and assigned to Zenith Radio Electronics Corporation, describes and claims a system for conserving power and prolonging life of high brightness display CRTs operated from vehicular battery sources. In that application the CRT filament heater circuit is operated at a low power level during standby and is switched to operate at a normal level responsive to receipt of a signal indicating that data is to be displayed. The present system is directed to the same general problem solved by the system of the copending application.